The need for high specific capacities and specific energies has led to the study of various metal-element batteries such as lithium-sulfur, metal-oxygen, lithium-oxygen, and the like. Batteries made with lithium-oxygen, lithium-air and lithium with other gas mixtures containing oxygen are particularly attractive due to the low atomic number and density and high reducing capability of elemental lithium, and a lithium oxygen battery could potentially have a theoretical specific energy three to five times greater than conventional lithium ion batteries.
FIG. 1 is a schematic representation of a lithium oxygen battery 10, in which elemental lithium metal is oxidized at an anode 12 to form lithium ions (Li+) and electrons (e−). The electrons flow about an electric circuit 15 across a load 16 to do electric work, and the lithium ions migrate across an electrolyte 18 to reduce oxygen (from air) at a porous carbon, metal or metal oxide cathode 14. Optional metal catalysts 20 can be incorporated into the cathode 14 to enhance oxygen reduction kinetics and increase the specific capacity of the cathode.
The electrolyte 18 transports lithium ions from the anode 12, and may be selected from solid state lithium ion conducting materials, organic electrolytes, aqueous electrolytes, and combinations thereof. For example, in an organic electrolyte, gaseous oxygen is reduced to form lithium peroxide at the cathode 14, and in aqueous solution reduction of gaseous oxygen to lithium hydroxide occurs at the cathode 14. If an aqueous electrolyte 18 is employed in the battery 10, a lithium ion conducting membrane 22 (LICM) may be used to protect the lithium anode 12 from water, and the membrane 22 may be placed in close contact with the anode 12. If an organic electrolyte 18 is used in the battery 10, the LICM 22 in principle is not required, but may be useful to keep oxygen and any introduced water and CO2 away from the lithium anode 12. In some embodiments the battery 10 may include a multi-electrolyte cell in which the electrolyte solutions in contact with the anode 14 and the cathode 12 are different. In the multi-electrolyte cell, a first electrolyte 18A resides between the cathode 12 and the LICM 22, and a second electrolyte 18B, different from the first electrolyte 18A, resides between the LICM 22 and the cathode 14. This configuration allows the solvents 18A, 18B to be optimized for the electrode with which it is in contact, thus not requiring a single material to deliver both oxidative and reductive resistance.